Add SwiftLint workflow.

Signed-off-by: Ivan Sein <ivan@nextcloud.com>

.github/workflows/swiftlint.yml

@@ -0,0 +1,20 @@
+name: SwiftLint
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master  
+
+jobs:
+  SwiftLint:
+    runs-on: ubuntu-latest
+    
+    steps:
+     - uses: actions/checkout@v2
+       
+     - name: GitHub Action for SwiftLint
+       uses: norio-nomura/action-swiftlint@3.2.1
+